1. Field of the Invention
The invention relates to a light emitting system and a voltage conversion device.
2. Description of the Related Art
Referring to FIG. 1, a conventional light emitting system 1 is shown to include a voltage conversion device 11, a processor 12, a variable current source 13 and a light emitting diode (LED) unit 14. The voltage conversion device 11 is coupled to an alternating-current (AC) power source 10 for receiving an AC voltage, and converts the AC voltage into a direct-current (DC) voltage Vo serving as a working voltage of the processor 12. The processor 12 generates an adjustment signal according to the DC voltage Vo. The variable current source 13 is coupled between the processor 12 and a ground node, and receives the adjustment signal from the processor 12, so as to generate a driving current Io for driving the LED unit 14. The voltage conversion device 11 includes a rectifier circuit 15, a voltage reducing circuit 16 and an output circuit 17.
The rectifier circuit 15 is coupled to the AC power source 10 for receiving the AC voltage, and has a first rectifier output O1 coupled to the LED unit 14, and a second rectifier output O2. The rectifier circuit 15 rectifies the AC voltage, and generates a rectified voltage VRE across the first and second rectifier outputs O1, O2.
The voltage reducing circuit 16 is coupled to the first and second rectifier outputs O1, O2 for receiving the rectified voltage VRE, and has an output O3 that provides a reduced voltage associated with the rectified voltage VRE.
The output circuit 17 is coupled between the output O3 of the voltage reducing circuit 16 and the second rectifier output O2 for receiving the reduced voltage, so as to generate the DC output voltage Vo that is provided to the processor 12.
Such a conventional light emitting system 1 has the following drawbacks:
1. High power consumption and short service life: Since the rectified voltage VRE is mainly across the voltage reducing circuit 16, the voltage reducing circuit 16 may be easily damaged due to high power consumption, resulting in a short service life.
2. Low conversion efficiency: Since the rectified voltage VRE is mainly across the voltage reducing circuit 16, the DC output voltage Vo that is outputted by the output circuit 17 according to the reduced voltage may be limited, resulting in low conversion efficiency.
3. Waste of current: Since the variable current source 13 is grounded, the driving current Io directly flows to the ground, resulting in waste of current.